Don't show negative durations on buffs/debuffs

diff --git a/oUF_P3lim.lua b/oUF_P3lim.lua
index fca5da6..f245428 100644
--- a/oUF_P3lim.lua
+++ b/oUF_P3lim.lua
@@ -101,7 +101,7 @@ end

 local function UpdateAura(self, elapsed)
 	if(self.expiration) then
-		self.expiration = self.expiration - elapsed
+		self.expiration = math.max(self.expiration - elapsed, 0)

 		if(self.expiration > 0 and self.expiration < 60) then
 			self.Duration:SetFormattedText('%d', self.expiration)